1. Field of the Invention
This invention relates to the field of spectroscopy, and more particularly fluorescence imaging.
2. Description of Related Art
Many studies and applications make use of a fluorescence signal, particularly in biology. The weakness of the fluorescence signal is a major technical stumbling block. In most applications and studies, the quantity of fluorescent markers or fluorophores is namely often limited. It is important to increase sensitivity in the case of biochips for example, or when monitoring small quantities of molecules in cells. The increase of the fluorescence signal is also sought for molecules with a low fluorescence quantum efficiency.
At the moment, needs are essentially satisfied by specific observation techniques, and particularly lighting techniques using evanescent waves in total reflection. Furthermore, the weakness of the fluorescence signal makes it necessary to use additional amplification techniques, frequently expensive, requiring a large amount of time and introducing amplification biases that have to be controlled. A typical case is DNA chips for which a polymerase chain reaction (PCR) amplification step is often essential. Many types of supports have been developed to enhance the fluorescence signal and minimise the need for such an amplification step.
Some supports as those described in U.S. Pat. No. 5,866,433 are based on enhanced fluorescence induced by the presence of metallic nanoparticles under a transparent and inert separating layer.
There are also mirror type supports with a transparent spacing layer, Supports proposed in U.S. Pat. No. 4,649,280 are perfect mirrors covered with a transparent spacing layer. U.S. Pat. No. 5,006,716 proposes mirrors with a periodically corrugated conducting layer so as to induce fluorescence in a preferential direction, therefore requiring excitation and detection along a clearly defined direction. Therefore specific excitation and observation configurations are necessary to use this type of support.
However all these supports that enable a certain enhancement of the fluorescence signal have a number of disadvantages, particularly related to the specific nature of the detection devices or their particular usage configuration. Thus, the use of such supports remains complex and/or expensive.
Therefore it is an object of the invention to provide a simplified fluorescence detection device that at least overcomes at least one of the above-mentioned disadvantages.